xsane says failed to open device hpaio:/net/ device busy

I'm running Ubuntu 6.10 with HPLIP 1.6.9 and can't scan from an HP-2840. But I am able to print to it without problem.
xsane sees it (actually, it sees two of the same device), but when I select one and click OK, it responds with "Failed to open device `hpaio:/net/HP_Color_Laserjet_2840?ip=192.168.56.13': Device busy.

Copyright (c) 2003-6 Hewlett-Packard Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

The scanner used to work from both Windows and Debian, but then I
switched to Ubuntu and it hasn't worked since. It also no longer works
from Windows.

There's no hp-check on this system. I believe it doesn't come with
Ubuntu. However, hp-info did find the printer, and its output is in the
original report. Also, note that xsane appears to see the printer, but
can't communicate with it.

Copyright (c) 2001-7 Hewlett-Packard Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

Note: hp-check can be run in three modes:
1. Compile-time check mode (-c or --compile): Use this mode before compiling
the HPLIP supplied tarball (.tar.gz or .run) to determine if the proper
dependencies are installed to successfully compile HPLIP.
2. Run-time check mode (-r or --run): Use this mode to determine if a distro
supplied package (.deb, .rpm, etc) or an already built HPLIP supplied tarball
has the proper dependencies installed to successfully run.
3. Both compile- and run-time check mode (-b or --both) (Default): This mode
will check both of the above cases (both compile- and run-time dependencies).

Checking for dependency: cups-devel- Common Unix Printing System development files...
error: NOT FOUND! This is a REQUIRED/COMPILE TIME ONLY dependency. Please make sure that this dependency is installed before installing or running HPLIP.
To install this dependency, execute this command:
sudo apt-get install --yes --force-yes libcupsys2-dev cupsys-bsd

Checking for dependency: libcrypto - OpenSSL cryptographic library...
error: NOT FOUND! This is a REQUIRED dependency. Please make sure that this dependency is installed before installing or running HPLIP.
To install this dependency, execute this command:
sudo apt-get install --yes --force-yes openssl

Checking for dependency: libjpeg - JPEG library...
error: NOT FOUND! This is a REQUIRED dependency. Please make sure that this dependency is installed before installing or running HPLIP.
To install this dependency, execute this command:
sudo apt-get install --yes --force-yes libjpeg62-dev

Checking for dependency: libnetsnmp-devel - SNMP networking library development files...
error: NOT FOUND! This is a REQUIRED dependency. Please make sure that this dependency is installed before installing or running HPLIP.
To install this dependency, execute this command:
sudo apt-get install --yes --force-yes libsnmp-dev

Checking for dependency: libtool - Library building support services...
error: NOT FOUND! This is a REQUIRED/COMPILE TIME ONLY dependency. Please make sure that this dependency is installed before installing or running HPLIP.
To install this dependency, execute this command:
sudo apt-get install --yes --force-yes libtool

Checking for dependency: libusb - USB library...
error: NOT FOUND! This is a REQUIRED dependency. Please make sure that this dependency is installed before installing or running HPLIP.
To install this dependency, execute this command:
sudo apt-get install --yes --force-yes libusb-dev

Checking for dependency: make - GNU make utility to maintain groups of programs...
OK, found.

Checking for dependency: python-devel - Python development files...
error: NOT FOUND! This is a REQUIRED/COMPILE TIME ONLY dependency. Please make sure that this dependency is installed before installing or running HPLIP.
To install this dependency, execute this command:
sudo apt-get install --yes --force-yes python2.5-dev

Checking for dependency: SANE - Scanning library development files...
error: NOT FOUND! This is a REQUIRED/COMPILE TIME ONLY dependency. Please make sure that this dependency is installed before installing or running HPLIP.
To install this dependency, execute this command:
sudo apt-get install --yes --force-yes libsane-dev

'hpaio' in '/etc/sane.d/dll.conf'...
error: Not found. SANE backend 'hpaio' NOT properly setup (needs to be added to /etc/sane.d/dll.conf).

Checking output of 'scanimage -L'...

No scanners were identified. If you were expecting something different,
check that the scanner is plugged in, turned on and detected by the
sane-find-scanner tool (if appropriate). Please read the documentation
which came with this software (README, FAQ, manpages).

Marcel Straub's answer worked in my scenario (HP Color LaserJet 2840 / Sane on both Ubuntu 10.04 and CentOS 5.5).
The error would either be "device busy" or "Error during device IO" when trying to connect to the JetDirect hpaio:/net/ etc. backend.
(re-)enabling SNMP write solved the problem.